Cover

In telecommunication, cover is the technique of concealing or altering the characteristics of communications patterns for the purpose of denying an unauthorized receiver information that would be of value.

Note: Cover is a process of modulo two addition of a pseudorandom bit stream generated by a cryptographic device with bits from the control message.

Source: from Federal Standard 1037C and from MIL-STD-188

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In philately a cover is an envelope or package[?], typically with stamps that have been cancelled.

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In pop music a cover is a new version of a previously recorded song. Virtually all pop musicians play covers, as tributes to their mentors, or on the theory that what was a hit before may be a hit again, or to gain credibility from their comparison with the original. A cover band may play only music by one more prominent band or may play music from many sources.

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According to the Oxford English Dictionary, the original sense of the verb and noun cover was "to hide from view" as in its cognate covert. Except in the limited sense of "cover again", the word recover is unrelated and is cognate with recuperate.